From d5a744b0909c4b2bec397ae4dcd43b56aba355c6 Mon Sep 17 00:00:00 2001
From: HampusM <hampus@hampusmat.com>
Date: Tue, 19 May 2026 00:12:11 +0200
Subject: feat(ecs): add error handling

---
 ecs/examples/error_handling.rs | 79 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 ecs/examples/error_handling.rs

(limited to 'ecs/examples')

diff --git a/ecs/examples/error_handling.rs b/ecs/examples/error_handling.rs
new file mode 100644
index 0000000..dc34c5f
--- /dev/null
+++ b/ecs/examples/error_handling.rs
@@ -0,0 +1,79 @@
+use ecs::error::Error;
+use ecs::event::component::{Changed, EventMatchExt};
+use ecs::pair::Pair;
+use ecs::phase::UPDATE;
+use ecs::query::Query;
+use ecs::system::observer::Observe;
+use ecs::{Component, World, error};
+use tracing::level_filters::LevelFilter;
+use tracing_subscriber::EnvFilter;
+use tracing_subscriber::fmt::time::ChronoLocal;
+use tracing_subscriber::layer::SubscriberExt;
+use tracing_subscriber::util::SubscriberInitExt;
+
+#[derive(Component)]
+struct State
+{
+    value: u32,
+}
+
+fn do_something_fallible(query: Query<(&mut State,)>) -> Result<(), Error>
+{
+    for (mut state,) in &query {
+        state.value += 1;
+
+        state.set_changed();
+
+        if state.value > 3 {
+            return Err(error!("Invalid state value {}", state.value));
+        }
+    }
+
+    Ok(())
+}
+
+fn handle_state_changed(observe: Observe<Pair<Changed, State>>) -> Result<(), Error>
+{
+    for evt_match in &observe {
+        let state = evt_match.get_ent_target_comp();
+
+        if state.value > 3 {
+            return Err(error!("Invalid state value {}", state.value));
+        }
+
+        tracing::info!("State has valid value {}", state.value);
+    }
+
+    Ok(())
+}
+
+fn main()
+{
+    tracing_subscriber::registry()
+        .with(
+            tracing_subscriber::fmt::layer()
+                .with_timer(ChronoLocal::new("%T%.6f".to_string())),
+        )
+        .with(
+            EnvFilter::builder()
+                .with_default_directive(LevelFilter::DEBUG.into())
+                .from_env()
+                .unwrap(),
+        )
+        .init();
+
+    let mut world = World::new();
+
+    world.set_err_handler(ecs::error::err_handler_log_error);
+
+    world.create_entity((State { value: 0 },));
+
+    world.register_system(*UPDATE, do_something_fallible);
+
+    world.register_observer(handle_state_changed);
+
+    world.step();
+    world.step();
+    world.step();
+    world.step();
+}
-- 
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